Flexible coupling

ABSTRACT

The disclosed flexible coupling is joining sections of rigid conduit, with provision for angular, axial and lateral flexiblity, and static sealing against fluid leakage. The conduit sections are interconnected by a tubular metal bellows which has the shape of a truncated cone for applications requiring increase fatigue life. The bellows is secured to ferrules either welded or swaged to the conduit ends. An E-seal, O-ring or similar seal is provided in a recess in one ferrule abutting the end of the metal bellows to provide a sealing means which does not flex despite lateral, axial and angular flexure of the bellows. The bellows is secured to the respective ferrules by a coupling nut at one end and by welding at the other end. In an alternate embodiment the said other end of the bellows is swaged in place between the ferrule and the conduit section.

United States Patent 1151 3,

Mischel [4 1 Sept. 19, 1972 [s41 FLEXIBLE COUPLING FOREIGN PATENTS 0RAPPLICATIONS Inventor: H w M h l, n D g 866,411 5 1941 'France ..285/226Caiif- 609,137 11/1960 Canada ..285/226 [73] Assignee: AVICACorporation, Middletown,

R.l. Primary ExaminerAndrew V. Kundrat 221 Filedzl Sept. 4, 1970 21App1.No.: 69,660 57 ABSTRACT Related US. Application Data The disclosedflexible coupling is joining sections of rigid conduit, with provisionfor angular, axial and [63] 3 gfi g of May lateral flexiblity, andstatic sealing against fluid leakage. The conduit sections areInterconnected by a 52 US. (:1 ..285/226, 285/299 tubular metal be1lwswhidi has the shape 51 Int. Cl ..F16] 27/10 Gated Cone for applicationsrequiring increase fatigue 5 Field f Search 235 22 27 2 229, life. Thebellows is secured to ferrules either welded 285/300, 301 or swaged totheconduit ends. An E-seal, O-ring or similar seal is provided in arecess in one ferrule [56] References Cited abutting the end of themetal bellows to provide a sealing means which does not flex despitelateral, axial UNITED STATES PATENTS and angular flexure of the bellows.The bellows is 2,014,355 9/1935 Hussman ..285/226 secured to therespective ferrules by a coupling nut at 2,196,676 4/1940 Johnson etal....285/226 one end and by welding at the other end. In an al- 3,i69,785temate embodiment the said other end of the beflows 3,43 Tones X isswaged in place between the ferrule and the conduit 1,726,483 8/ 1929Giesler ..285/300 X Section. 2,485,370 10/1949 Dreyer ..285/228 282,9678/1883 Duffy ..285/226 10 Claims, 6 Drawing Figures 6a i4 6 a! K JFLEXIBLE COUPLING CROSS REFERENCE TO RELATED APPLICATION This is acontinuation-in-part of application Ser. No.

822,958, filed May 8, 1969 and now US, Pat. No. 5

BACKGROUND OF THE INVENTION Flexible couplings for rigidconduit such aspipe or also permit a degree of leeway during installation so thatprecise dimensional control of components is not needed. One commonapplication of flexible couplings is in connecting rigid components ofaircraft fuel and pneumatic systems.

. Prior art flexible couplings, however, have suffered from severaldisadvantages. One shortcoming has been in the degree of flexibilityafforded. Some couplings have pennitted only axial movement, others onlylateral or angular movement. For aircraft and similar uses however, itis desirable to have a degree of flexi-. bility in axial, angular andlateral directions, i.e., substantially universal flexibility tocompensate for both expansion and contraction, dimensional imperfectionsand expected and unexpected stresses due to shock and acceleration.

Another problem arises with respect to the seals which are used in theflexible coupling to prevent leakage of the fluid in the system. Inprior art couplings these seals have been of the dynamic type, that is,they have had to flex along with the coupling. However,the requirementof flexibility is a limiting factor. It is difficult if not impossibleto find sealing materials which retain theirsealing'qualities and alsotheir flexibility over a wide range of temperatures and for extended 40periods. Loss of resilience dueto temperature, aging and fatigue havecaused so-called dynamic seals to be unreliable and therefore a weaklink in the conduit system.

Also, prior flexible couplings of the type containing bellows are oftensubject to early fatigue failure in the bellows. This is believed due tothe fact that flexure is often substantially confined to one or theother ends of the bellows. Accordingly relatively few of the bellowsconvolutions bear the entire brunt of stress cycling.

Additionally, prior art flexible couplings have often been complicated,bulky and heavy, and therefore difficult to install and repair.

Accordingly, representative objects of the present intions hereinafterset forth, and the scope of the invention will be indicated in theclaims.

SUMMARY OF THE INVENTION The present invention relates to a flexiblecoupling for rigid conduit and more particularly to a flexible couplingpermitting axial, angular and lateral flexibility and providing forincreased fatigue life and static sealing against fluid leakage.

The coupling comprises a tubular, flexible metal bellows secured toferrules welded, swaged or otherwise secured to adjacent ends of theconduit sections to be joined. The metal bellows provides an effectivemeans of achieving relative axial angular and lateral flexibilitybetween conduit sections while providing continuity of flow through theconduit.

For increased fatigue life the metal bellows is pro- I vided in theshape of a truncated cone. This is done by gradually decreasing theouter diameter of successive convolutions toward one end of the bellows.Since the smaller diameter convolutions are more resistant to flexure,that end of the bellows is then positioned at the area of maximum stressin the coupling. Accordingly, the stress tends to be more evenlydistributed along the bellows and flexure tends to occur over the entirebellows length rather than being confinedv to the most highly stressedend. This is believed to be the mechanism which leads to greater fatiguelife in the coupling of the invention, although the invention is not tobe limited to any specific theory of operation.

The bellows is preferably secured to the respective ferrules by a pairof rings which are mounted in opposite end convolutions of the bellows;one, a welding ring, is preferably formed in two halves so as to bereadily insertable in one end convolution. The welding ring is thenwelded to an abutment on one ferrule to secure that end of the bellowsin place. The other ring is urged against its ferrule by a coupling nutwhich screws onto the ferrule. Sufficient clearance is left betweenmating parts of the coupling so that a desired amount of axial, angularand lateral flexing can occur.

The construction of the flexible coupling makes as sembly-relativelysimple. The bellows with its pair of rings and the ferrule to which thewelding ring is attached may be provided as a prefabricatedsub-assembly. Assembly then comprises welding, swaging or otherwisesecuring the ferrule on the sub-assembly to one conduit segment,similarly securing the other ferrule to the opposite conduit segment andthen completing the coupling by screwing on the coupling nut.

The coupling may also be provided with static fluid seals preferablycomprising flexible metal seals or 0- rings recessed in the ferrulesurfaces abutting the bellows ends. Since the seals are static, that is,undergo substantially no flexing during either axial or angular flexureof the bellows, they are highly reliable and long lasting. Moreover, theproblem of maintaining seal flexibility at elevated or low temperatures,and over long periods of use is greatly reduced since the seals undergosubstantially no flexing. I

The structure of the invention also provides a more compact andlightweight coupling, further simplifying assembly and disassembly andenhancing its use in applications such as aircraft.

BRIEF DESCRIPTION OF THE DRAWINGS For a'fuller understanding of thenature and objects of the invention, reference should be had to thefollowing detailed description taken in. conjunction with theaccompanying drawings, in which: i I I FIG. 1 is a side elevation viewof the flexible coupling of the invention joining two sections of rigidcylindrical pipe.

FIG. 2 is a left end view of the coupling of FIG. 1. I

FIG. 3 is an enlarged, partial sectional view of the coupling takenalong line 33 of FIG. 2.

FIG. 4 isan enlarged, partial sectional view of another embodiment ofthe coupling shown in FIG. 3 wherein the ferrules are swaged to theunderlying conduit sections.

FIG. 5 is an enlarged, partial sectional view. of another embodiment ofthe coupling shown in FIG. 4 wherein one end of the bellows is swagedbetween a ferrule and the underlying conduit section.

FIG. 6 is an enlarged, partial sectional view of another embodiment ofthe coupling shown in FIG. 3.

Similar reference charactersrefer to similar parts throughout theseveral views of the drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIG. 1, theflexible coupling 10 of the invention is shown interconnecting twosegments 12 and 14 of cylindrical pipe conduit. It can be seen,

however, thatvarious types and shapes of conduit can be joined byflexible coupling 10 andit is not intended that the invention be limitedto a cylindrical pipe coupling.

As shown in FIG. 3, coupling 10 comprises a pair of ferrules l6 and 18affixed to respective adjacent ends of conduit 12 and I4. Ferrules 16and 18 may be secured to the conduit ends by welding as shown.Alternatively, the ferrules may be secured by swaging as shown in FIG.4, and for this purpose are provided with interior grooves 20. Uponswaging, grooves 20 interlock with the surface of the conduit as shownin FIG. 4 to form a secure and fluid tight connection. For otherapplications, ferrules l6 and 18 may be secured by a brazed, soldered,threaded or sweated joint, or the like.

Ferrule l6, herein termed a female ferrule, is provided with anupstanding abutment 22 adjacent the open end of its conduit segment 12.Ferrule 18, herein termed a screw adapter ferrule, differs from ferrule16 in that it is provided with a larger diameter upstanding flange 24adjacent the open end of its respective conduit segment 14. Flange 24 isalso preferably threaded on its outer peripheral surface 26. Ferrule 18is further provided with an annular recess 28 on its surface 30. Recess28 forms part of a static seal for preventing fluid leakage from theinterior of the conduit as is more fully discussed hereinafter. I

The two segments 12 and 14 of the conduit are inter-. connected by atubular member which is flexible in axia], angular and lateraldirections. Preferably, as shown in the drawings, the flexible tubularconnector comprises a metal bellows 32. The material from which bellows32 is formed and the number of convolutions therein may vary dependingupon the material conveyed by the conduit, the operating conditions, andthe degree of flexibility desired.

As shown in FIG. 6, bellows 32 may be of a conventional type wherein theconvolutions are all equal in diameter. As previously discussed,however, such a bellows construction may be subject to early fatiguefailure and accordingly is preferably used in applications where thestress levels are low.

Most preferably bellows 32 takes the form of a trun cated cone as shownin FIGS. 3 and 4. The truncated cone shape is' the result of a decreasein the outer diameter of successive bellows convolutions looking fromleft to right in the drawings. It will be noted however that the innerdiameters of the bellows convolutions remain equal so as to provide asubstantially constant diameter passage for the flow of fluid throughthe coupling. As previously discussed, the provisionof a bellows in theform of a truncated cone increasesth'e fatigue life thereof by causingstresses and flexure to be more evenly distributed over the length ofthe bellows.

Bellows 32 is secured at one end to ferrule 16 by means of a weldingring 34 as shown in FIGS. 3,4 and 6. Welding ring 34 is annular andpreferably formed in two l semicircular portions to facilitate themounting thereof within the last convolution 36 at one end of bellows32. Once mounted in convolution 36, welding ring 34 is pressed againstthe flat surface 38 of abutment 22, clamping the bellows end 36atherebetween. While held in this position, the tapered outer periphery40 of ring 34 is then welded to abutment 22, most commonly by an arcwelding procedure, to fixedly secure that-end of the bellows to ferrule16. Preferably an annular cutout 44 is provided on the surface ofabutment 22 adjacent outer periphery 40 of welding ring 34. The purposeof cut-out 44 is to separate the bulk of abutment 22 from the weld areaso that it does not act as a heat sink and adversely affect the qualityof the weld. .The welded end of bellows 32 thus forms a static, fluidtight connection to ferrule 16.

Still referring to FIGS. 3,4 and 6 a secondring 46R- mounted in the lastconvolution 48 at the opposite end of bellows 32. Ring 46 is preferablymounted by bending convolution 48 around the inner diameter flange 50thereof. Accordingly, ring 46 need not be split or formed in two partsas is welding ring 34. The outer diameter portion 52 of ring 46 isthickened and provided with a beveled surface'54 to cooperate with themating surface of a coupling nut in order to secure that end of bellows32 in place. 7

As heretofore discussed, bellows 32 with ferrule 16 secured to one endby welding ring 34, and with ring 46 mounted at the other end withinconvolution 48, may be prefabricated asa complete sub-assembly. Thissimplifies final assembly of the coupling, and permits maintenance of asupply of such sub-assemblies as replacements should the coupling bedamaged or otherwise fail.

Coupling nut 56 completes the assembly of flexible coupling 10 as shownin FIGS. 3, 4 and 6. Nut 56 preferably comprises a threaded interiorportion 58 which is threaded over the corresponding threaded portion 26of ferrule 18. A skirt portion 60 extends from threaded portion 58 andacts as a protective cover over the bellows 32. A beveled surface 62 isprovided at the interior of nut 56 between threaded portion 58 and skirt60. It can be seen that as coupling nut 56 is threaded onto ferrule 18,beveled portion 62 engages the beveled surface 54 of ring 46 urging itagainst surface 30 of ferrule 18 to secure bellows 32 in positionbetween conduit segments 12 and 14. Alternatively, nut 56 may be securedto ferrule 18 by clamping or bolting.

Protective skirt 60 terminates in an overhanging lip 64 which furtherprotects the interior of the flexible coupling from damage due toforeign objects. It is important however, that sufficient clearance beleft both between lip 64 and abutment 22, and between lip 64 and thewelded or swaged portion of ferrule 16 so that a desired amount ofaxial, angular and lateral movement can occur between conduit segments12 and 14. The clearance provided for this purpose can be clearly seenin FIGS. 3, 4 and 6.

As shown in FIGS. 1, 3 and 6 the outer surface of coupling nut 56 may beprovided with a plurality of indentations 66 which will accommodate aspanner wrench for purposes of tightening nut. 56. Altematively, as withthe embodiments shown in FIGS. 4- and 5, the outer surface of couplingnut 56 may be knurled or otherwise roughened to facilitate manualthreading thereof. Additionally or alternatively, theouter surface ofskirt 60 may be knurled or roughened for manual threading.

Once in position, coupling nut 56 is preferably lockwired in place toprevent its accidentally being loosened. For this purpose a pair ofdrilled through holes 68 and 70 are provided in adjacent portions ofcoupling nut 56 and the flange 24 of ferrule 18 (FIGS. 3-6). Afterassembly of coupling 10, a lockwire (not shown) may be threaded throughholes 68 and 70 and twisted to secure the assembly. t

The flexible coupling may also be provided with-sealing means adjacentring 46 to prevent fluid leakage from inside the conduit. As shown inFIGS. 3-6, a flexible sealing member 72 is placed within the annularrecess 28 in ferrule 18. For high pressure applications member 72preferably comprises a flexible metal seal having the configurationshown in FIGS. 3 and 6 or some other suitable configuration. The metalseal may be plated with silver and is given suflicient flexibility forstaticsealing under operating conditions. Altematively, for lowerpressure applications, member 72 is preferably an O-ring (FIG. 4). Forsome applications a gasket or similar suitable static seal may be used.

As shown in the drawings, when flexible coupling 10 is assembled the end74 of bellows 32 is pressed tightly against member 72 to form aneflective seal. Significantly, it can be seen that despite any axial,angular or lateral flexure which bellows 32 may undergo, member 72 isnot required to flex, and undergoes no further distortion than that dueto the pressure exerted during assembly.

Member 72 in place in recess 28 thus forms a static sealing means. Sincesubstantially no flexure is required of member 72 in use, the problemsdue to loss of flexibility from aging, temperature change and fatiguecommon in dynamic seals is essentially eliminated. The coupling of theinvention is therefore highly attractive for use in cryogenic and veryhigh temperature environments. Prior art flexible couplings have notbeen useful in these environments because the dynamic seals thereof havelacked sufficient resiliency at these extrerne temperatures.

Although associated with a dynamic member, that is bellows 32, the sealformed by member 72 is'as reliable as any other static seal in theconduit system, such as that in a rigid pipe'joint. Further, the expensedue to seal maintenance and replacement common to prior art structuresis to a large degree eliminated by the present invention.

Another embodiment of the invention is shown in FIG. 5. The embodimentof FIG. 5 is substantially identical in all respects to the embodimentof FIG. 4 except for the elimination of the welding ring and'the cutoutportion of abutment 22. Instead of being welded in place by means of awelding ring, the left end 74 of bellows 32 as shown in FIG. 5 is madesomewhat longer and extended out perpendicular to the convolutions.

End 74 is then placed between conduit segment 12 and previouslydiscussed, fluid tight. Alternatively to the bellowsshape shown, a moreconventional bellows of the type shown in FIG- 6 may be used in theembodiment of FIG. 5. Althoughthe right end of bellows 36 in theembodiment ofFIG. 6 is sealed in the same manner as the right end in theembodiments of FIGS. 3, 4 and 6, it will be understood that this end mayalso be swaged between ferrule 18 and conduit segment 14 is desired.

As in the previously discussed embodiments, sufficient clearance is leftin the embodiment of FIG. 5 between overhanging lip 64 and abutment 22of ferrule 16, and between lip 64 and the swaged portion of ferrule 16so that a desired amount of axial, angular and lateral movement canoccur between conduit segments 12 and 14.

It will thus be seen that the objects set forth above, among those madeapparent from the preceding description, are efficiently attained and,since certain changes may be made in the above constructions withoutdeparting from the scope of the invention, it is intended that allmatter contained in the above description or shown in the accompanyingdrawings shallbe interpreted as illustrative and not in a limitingsense.

It is also to be understood that the followingclaims are intended tocover all of the generic and specific features of the invention which,as a matter of language, might be said to fall therebetween.

Having described my invention,what I claim as new and desire to secureby Letters Patent is: V

l. A flexible coupling for rigid conduit comprising, in combination: I

A. flexible tubular connector means comprising a tubular bellows,

B. a pair of ferrules mounted to adjacent ends of a pair of conduitsegments connected by said coupling comprising a female ferrule havingan upstanding abutment and secured to the end of one said conduitsegment, and ascrew adapter ferrule secured to the end of the other saidconduit segment, and C. fastening means for securing each end of saidbellows to said ferrules and providing clearance for relative axial,angular and lateral movement between said conduit segments comprising,I. an annular welding ring mounted in one end convolution of saidbellows adjacent said female ferrule, said welding ring being welded tosaid abutment with a portion of said one end convolution clampedtherebetween,

. 2. a second ring mounted within the other end convolution of saidbellows adjacent said screw adapter ferrule, and a coupling nutthreadedly engaged on said screw adapter ferrule and bearing againstsaid second ringto urge said second ring and associated end convolutionagainst a surface of said screw adapter ferrule, said second ring andcoupling nut having engaging complementary surfaces at the positionwhere said nut bears against said second ring.

2. A flexible coupling as defined in claim 1 wherein said tubularbellows has the shape of a truncated cone. 3. A flexible coupling asdefined in claim 1 including an annular recess in the surface of saidscrew adapter ferrule which bearsagainst said adjacent end convolution,and a sealing member in said recess forming a static seal against fluidleakage during flexure of said bellows. v

4. A flexible coupling as defined in claim 3 wherein said sealing membercomprises a flexible metal seal.

5. A bellows sub-assembly for use in a flexible coupling comprising, incombination:

A. flexible tubular connector means comprising a tubular bellows,

B. a femaleferrule having an upstanding abutment,

C.an annular welding ring mounted in one end convolution of said bellowsand being welded to said abutment with a portion of said one endconvolution clamped therebetween, and i v D. a second ring mountedwithin the opposite end convolution of said bellows, said second ringhaving a surface thereon adapted to engage with a complementary surfaceof a coupling nut when said sub-assembly is incorporated into saidflexible coupling.

6. A bellows sub-assembly as defined in claim 5 wherein said bellows hasthe shape of a truncated cone.

7. A flexible coupling for rigid conduit comprising, in

combination:

A. flexible tubular connector means comprising a tubular bellows,

1. said bellows having convolutions of decreasing outer diameter towardan end thereof to distribute stress and improve fatigue life,

B. a pair of ferrules mounted to adjacent ends of a pair of conduitsegments connected by said coupling, the ferrule at one end being ascrew adapter,

C. fastening means for securing each end of said bellows to saidferrules and providing clearance for relative axial, lateral and angularmovement between said conduit segments, said fastening means at said oneend comprising a ring mounted within the corresponding end convolutionof said bellows, and a coupling nut threadedly engaged on ther. co duitsegment end comp "sin a femalg,

errule aving an upstanding a ut I ent, sal fastening means at saidother-end comprising an annular welding ring mounted in the oppositeend.

convolution of said bellows and being welded to said abutment with aportion of said'opposite end convolution clamped therebetween, and

D. sealing means between said ring and said screw adapter ferruleforming a static seal against fluid leakage from withinsaid conduit,said static seal remaining static during flexure of said bellows.

8. Aflexible coupling as defined in claim 7 including i a cut-out in thesurface of said abutment adjacent said weld to improveweld quality.

9. Aflexible coupling asdefined in claim 7 wherein said welding ring isformed in two pieces to facilitate mounting in said opposite endconvolution.

10. A flexible coupling for rigid conduit comprising,

in combination: j r

A. flexible tubular connector means comprising a tubular bellows, v 1.said bellows having convolutions of decreasing outer diameter toward anend thereof to distribute stress and improve fatigue life,

B. a pair of ferrules mounted to adjacent ends of a pair of conduitsegments connected by said coupling, the ferrule at one end being ascrew adapter,

C. fastening means for securing eachend of said bellows to said ferrulesand providing clearance for relative axial, lateral and angular movementbetween said conduit segments, said fastening means at said one endcomprising a ring mounted within the corresponding end convolution ofsaid bellows, and a coupling nut threadedly engaged on said screwadapter ferrule and bearing against said ring to urge said ring andbellows convolution against a surface of said screw adapter ferrule,said ring and said coupling nut having engaging complementary surfacesat the position where said nut bears against said ring, said screwadapter ferrule having an annular recess in its surface which bearsagainst the said end convolution of said bellows, said sealing meanscomprising a flexible metal seal mounted in said recess and forming saidstatic seal against fluid leakage during flexure of said bellows, and

D. sealing means between said ring and said screw adapter ferruleforming a static seal against fluid leakage from within said conduit,said static seal remaining static during flexure of said bellows.

1. A flexible coupling for rigid conduit comprising, in combination: A.flexible tubular connector means comprising a tubular bellows, B. a pairof ferrules mounted to adjacent ends of a pair of conduit segmentsconnected by said coupling comprising a female ferrule having anupstanding abutment and secured to the end of one said conduit segment,and a screw adapter ferrule secured to the end of the other said conduitsegment, and C. fastening means for securing each end of said bellows tosaid ferrules and providing clearance for relative axial, angular andlateral movement between said conduit segments comprising,
 1. an annularwelding ring mounted in one end convolution of said bellows adjacentsaid female ferrule, said welding ring being welded to said abutmentwith a portion of said one end convolution clamped therebetween,
 2. asecond ring mounted within the other end convolution of said bellowsadjacent said screw adapter ferrule, and a coupling nut threadedlyengaged on said screw adapter ferrule and bearing against said secondring to urge said second ring and associated end convolution against asurface of said screw adapter ferrule, said second ring and coupling nuthaving engaging complementary surfaces at the position where said nutbears against said second ring.
 2. a second ring mounted within theother end convolution of said bellows adjacent said screw adapterferrule, and a coupling nut threadedly engaged on said screw adapterferrule and bearing against said second ring to urge said second ringand associated end convolution against a surface of said screw adapterferrule, said second ring and coupling nut having engaging complementarysurfaces at the position where said nut bears against said second ring.2. A flexible coupling as defined in claim 1 wherein said tubularbellows has the shape of a truncated cone.
 3. A flexible coupling asdefined in claim 1 including an annular recess in the surface of saidscrew adapter ferrule which bears against said adjacent end convolution,and a sealing member in said recess forming a static seal against fluidleakage during flexure of said bellows.
 4. A flexible coupling asdefined in claim 3 wherein said sealing member comprises a flexiblemetal seal.
 5. A bellows sub-assembly for use in a flexible couplingcomprising, in combination: A. flexible tubular connector meanscomprising a tubular bellows, B. a female ferrule having an upstandingabutment, C. an annular welding ring mounted in one end convolution ofsaid bellows and being welded to said abutment with a portion of saidone end convolution clamped therebetween, and D. a second ring mountedwithin the opposite end convolution of said bellows, said second ringhaving a surface thereon adapted to engage with a complementary surfaceof a coupling nut when said sub-assembly is incorporated into saidflexible coupling.
 6. A bellows sub-assembly as defined in claim 5wherein said bellows has the shape of a truncated cone.
 7. A flexiblecoupling for rigid conduit comprising, in combination: A. flexibletubular connector means comprising a tubular bellows,
 8. A flexiblecoupling as defined in claim 7 including a cut-out in the surface ofsaid abutment adjacent said weld to improve weld quality.
 9. A flexiblecoupling as defined in claim 7 wherein said welding ring is formed intwo pieces to facilitate mounting in said opposite end convolution. 10.A flexible coupling for rigid conduit comprising, in combination: A.flexible tubular connector means comprising a tubular bellows,